<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>买书练习</title>
  <script src="../vue.js"></script>
  <style>
    .red {
      color: red;
    }
  </style>
</head>

<body>
  <div id="app">
    <div>
      <p>请选择你要购买的书籍</p>
      <ul>
        <li v-for="(item,index) in arr" :key="index">
          {{item.name}}
          <span>
            <button @click="buy(index)">买书</button>
          </span>
        </li>
      </ul>
      <table border="1" width="500" cellspacing="0">
        <tr>
          <th>序号</th>
          <th>书名</th>
          <th>单价</th>
          <th>数量</th>
          <th>合计</th>
        </tr>
        <tr v-for="(item, index) in arr" :key="index">
          <th>{{index + 1}}</th>
          <th>{{item.name}}</th>
          <th>{{item.price}}</th>
          <th>{{item.count}}</th>
          <th>{{item.price * item.count}}</th>
        </tr>
      </table>
      <p :class="{red : totalPrice > 500}">总价格为:{{totalPrice}} </p>
    </div>
  </div>
  <script>
    const app = new Vue({
      el: '#app',
      data: {
        arr: [
          {
            name: "水浒传",
            price: 107,
            count: 0,
          },
          {
            name: "西游记",
            price: 192,
            count: 0,
          },
          {
            name: "三国演义",
            price: 219,
            count: 0,
          },
          {
            name: "红楼梦",
            price: 178,
            count: 0,
          },
        ],
      },
      methods: {
        buy(id) {
          this.arr[id].count++
        }
      },
      computed: {
        totalPrice() {
          return this.arr.reduce((prev, item) => prev + item.price * item.count, 0)
        }
      },
      watch: {

      }
    })
  </script>
</body>

</html>